I'm in the club high on purp with some shades on

Miley’s been smoking some “purple kush”, which is purple weed. The purple comes from low temperature conditions and harvesting late in the flowering stage, when the red chloroplasts show over the dying green ones. The purple color is commonly believed to be a sign of HIGH QUALITY.

Marijuana users are known to put on shades as well because of the red eyes they may experience whenever marijuana is smoked.

Miley’s is also referring to being high on purple drank. Purple drank is usually a mix of cough syrup and sprite. Other names for purple drank are: Sizzurp, lean & drank.

This is most likely not what she meant though since the ‘effect’ that ‘drank users’ experience is called ‘leaning’.